This proposed research is concerned with the relationship of time estimation and decision time to certain aspects of evoked potentials recorded from the scalp of normal humans. There have been several reports of cerebral potentials occurring shortly after the expected time of an absent stimulus when the absence provides salient information to the subject. Such events, called emitted potentials, are clear signs of endogenous brain processes, apparently dependent upon memory activity and internal timing mechanisms. These emitted potentials have been studied in a paradigm where the subject is required to guess, prior to a trial, whether the stimulus in question will occur and then must implicitly rely upon internally generated temporal information to determine whether the stimulus did occur. The hypothesis to be examined is that latency variations of the emitted potentials reflect variations in time estimation. The latency variation and other features of the emitted potentials will be investigated in the guessing paradigm and the results will be compared to explicit time estimation behavior observed under similar but separate experimental conditions. In order to isolate time estimation effects and directly study the relationship between emitted potentials and time estimation behavior, two further experiments will be conducted. The stimulus conditions will resemble those of the guessing paradigm, but the subjects' tasks will differ. In one experiment minimum modifications of the guessing paradigm are made to allow concurrent measurement of emitted potentials and behavioral signs of time estimation. In the second experiment explicit time estimation will be the only task of the subject. Emitted potentials and time estimates will be recorded concurrently and subjected to comparative analyses.